The Irish government should order an investigation into claims a garda officer may have helped target an IRA murder victim more than 20 years ago, the Democratic Unionist Party has said.

Jeffrey Donaldson said his party will be contacting the Fine Gael-led administration after evidence to the Smithwick Tribunal raised questions over the murder of Co Louth farmer Tom Oliver.

In July 1991 the father of seven was kidnapped, tortured and shot dead by the IRA, before his body was dumped north of the border at Belleek in Co Armagh. There was outrage at the time of his killing and his family rejected allegations he had been passing information on republicans to security forces in the Republic.

But a former British agent testifying at the Smithwick Inquiry into alleged garda collusion in the murder of two senior Royal Ulster Constabulary (RUC) members in 1989, also indicated that a garda officer had identified Mr Oliver to the IRA.

Mr Donaldson said his party now planned to lobby the Irish government on the murder of Mr Oliver following the claims of the agent known as Kevin Fulton.

"Based on the evidence that Kevin Fulton gave to the Smithwick Inquiry, I believe that there have been new revelations that need to be examined to determine whether they would assist the police in apprehending those who were responsible for the murder of Tom Oliver," said the Democratic Unionist MP.

"I am calling on the Irish government to initiate a review by the Garda of the police investigation south of the border and also involving the PSNI (Police Service of Northern Ireland)."

He said a review of the murder investigation in the south, and of the circumstances of the discovery of the murdered man's body on the northern side of the border, may determine whether a garda officer had helped initiate the killing.

The Smithwick Tribunal is investigating alleged Garda collusion in the murders of RUC officers Harry Breen and Bob Buchanan in south Armagh in 1989.

The Democratic Unionist Party has recently spoken to Taoiseach Enda Kenny about IRA murders in border areas and claims that the authorities failed to address republican violence at the height of the Troubles.